Tuesday, 23 August 2016

The striking flower arrangement shown above is by Jane Hass
and features two blooms of Strelitzia
reginae, commonly known as the Bird of Paradise Plant, or the Crane Flower.
These names were given to the plants because they reminded some observers of
the two birds, but only an avid Creationist would believe in such mimicry, or that they were devised for our visual pleasure. S. reginae is native to South Africa, where it grows on river banks
and in woodland clearings, and it was so attractive to collectors that seeds
have been exported widely and the plant grows well in warm climates. It is the official flower of the City of Los Angeles [1].

Each flower consists of bright orange sepals and darker
petals and these emerge from a spathe (the pointy section that looks like the beak
of the bird in our imagination). At the base of the petals is a nectary containing
sugars that change in their composition over time [2], although we do not know
the reason for this.

Nectar is produced by almost all flowering plants and provides
an attractant for animals that use it as an energy source and then collect
pollen that is transferred to another plant to ensure fertilisation. Most
commonly, the pollinators are insects and the plant loses sugars (produced abundantly
during photosynthesis), and some of the pollen (many bees collect this, for
example), but the mutualism between the plant and the pollinating insects is
clearly of benefit to both and is a very successful strategy. Insects are
not the only pollinators, however, and S.
reginae is fertilised by birds, with its pollen formed into threads and aggregates
[3] to enhance attachment and transmission. The most common pollinator is the
Cape Weaver (Ploceus capensis – see
below), that feeds on the pollen aggregates as well as the nectar and transfers
pollen on its feet while visiting another flower [4,5], with the rigid spathe
providing an ideal initial landing place.

Visits by weaver birds have described
by Hoffman et al. [6]:

Landing of the bird on the blue sheath-forming
petals exposes the hidden pollen to the feet of the bird, while the bird probes
the corolla tube with its beak and extends its tongue to reach the nectar.. ..
Once landed and feeding, these birds have been observed to seldom move their feet,
thus keeping self-pollination low.. .. As a consequence, the best place for the
bird to feed is also the best position for pollination.

Sunbirds (Cinnyris
spp.) also visit S. reginae plants,
but it is likely that they play little part in pollination and they are regarded
as "nectar thieves" [5]. As Coombs and Peter note [7]:

The nectary of S. reginae is covered by the convoluted
bases of the two fused petals forming a barrier to the opening of the corolla
tube.. ..The behaviour of sunbirds indicates that they are nectar thieves and
can manipulate the nectar barrier with their beaks to gain access to the nectar
without causing obvious damage to the flowers of S.reginae.

Pollination in S. reginae is thus an example of the evolution of a strategy that
depends on mutualism, with other species taking advantage of the "gifts" provided by the plant.

So what
happens when seeds are taken to other countries? An abundance of
imported seeds ensures that plants can be grown without the need for
fertilisation, but we now know that S.
reginae is pollinated by indigenous birds. The common yellowthroat of
southern North America (Geothlypis
trichas – see below), a type of warbler, feeds on nectar and, just as with
the weaver birds in Africa, picks up pollen on its feet. As Hoffman et al.
point out [6] it is unlikely that "adaptive floral changes have started
the association" in the very short time during which S. reginae have been grown in the USA, but the behaviour
of the warblers allowed them to discover the nectaries and release pollen on to
their feet and thus ensure fertilisation. All this mimicking an association
that evolved over very long time periods in South Africa where the plant is
endemic.

It is interesting to speculate on how yellowthroats
developed this behaviour. The bright sepals of S. reginae may be an attractant to many animals, including the
insects and other invertebrates on which the warbler feeds. Could it be that
the habit of feeding on nectar, and picking up pollen on the feet, happened
through successive visits of some birds to feed on insects; a behaviour that
became established in populations as a result of learning from other individuals?
Whatever its origins, it is another example of the wonder of evolution and of Natural
History.

Wednesday, 10 August 2016

The rich flora of southern Africa has provided us with many garden
plants, including members of the iris family that naturalise readily [1]. Among
the most popular of these plants is montbretia, or coppertips (Crocosmia x crocosmiiflora – a cross of C. aurea and C. pottsii [2]), the result of horticultural inter-breeding and now
popular world-wide for its attractive foliage and, especially, its orange-red
flowers.

Montbretia has two methods of reproduction: fertilisation of
the flowers by insects (and, in some closely-related Crocosmia plants, by wind or humming birds) to produce seeds; and vegetative
reproduction, where each plant produces stolons, or runners, that form new
plants when roots and leaves grow from nodes.

Flowering occurs over a period of days, with the first
flowers at the base of the spike and then sequentially towards the tip, the production
of seeds following the same sequence. This habit ensures that some flowers are
likely to be fertilised during optimal conditions for pollination, and the
seeds, similarly, are produced over time to ensure that dispersal is optimal. This
flowering habit is a feature of many plants, but it is important to recognise
that it evolved to the advantage of the plant a very long time before humans
appeared. It was not designed by, and for, gardeners.

Vegetative growth by stolons ensures local colonisation and
many gardeners like to divide dense clumps, as they tend to choke off other
plants (a measure of the success of the strategy). Each individual montbretia
grows from a corm and this develops after the successful germination of seeds
and the growth of the first colonising plant. It is likely that the casual
disposal of corms, rather than the spread of seeds, allowed montbretia (coppertips)
to be such a successful coloniser of natural habitats, frequently forming large
and vivid clumps on embankments and in coastal regions [2]. When established,
its growth habit ensures its spread and it may now be regarded by some as a
"wild flower".

Each corm is a store of starch grains produced synthetically
after photosynthesis and this store allows the growth of leaves and stems at
the beginning of the growing season. It is also used in shorter time scales to
allow the efficient metabolism of the plant. Starch grains that are stored by
plants for months often have their surface eroded [3], resulting from the
action of naturally-occurring enzymes involved in releasing easily-metabolised sugars
from the more complex starch. Among these is α–amylase and this enzyme is disabled in montbretia corms by the
presence of a compound called montbretin. This ensures that starch grains are
retained in good condition during resting phases, montbretin being of less
significance when starch is being metabolised.

The presence of montbretin, the metabolism of the plant, the
succession of flowers and seeds, and the vegetative spread by stolons, are all
extraordinary adaptations that make montbretia such a successful plant and an
effective invader. In addition, montbretia has recently received attention in
the world human health, something which always results in wide publicity. It
has been discovered that montbretin not only serves to protect starch grains
from the action of α–amylase in
Crocosmia corms, but may also inhibit
the action of these enzymes in humans, something that offers the possibility of
new drug treatments against diabetes [4]:

Type 2 diabetes mellitus is a
condition that affects well over 320 million people worldwide and is closely
associated with obesity. Among the oral antidiabetic drugs used for its
treatment are the α-glucosidase
inhibitors, which prevent hyperglycosemia by slowing digestion of starch and
malto-oligosaccharides in the gut. Partial hydrolysis of starch is accomplished
by salivary α-amylase, with
principal cleavage provided by human pancreatic α-amylase (HPA) within the gut, generating linear and branched
malto-oligosaccharides. These in turn are broken down to glucose by α-glucosidases that are anchored in the
epithelium of the small intestine..

..Selective inhibition targeted at
only HPA, the enzyme at the top of the starch digestion pyramid, could be used
to quantitatively modulate blood glucose levels by restricting or even shutting
down starch degradation, thereby minimizing the specificity problems that arise
with currently available α-glucosidase
inhibitors.

This is written in the technical language of a scientific
paper, but Williams, Zhang et al. [4] then describe the selective nature of
montbretin A (MbA) and its possible value in medicine:

Because MbA is such a potent
inhibitor and is easily isolated from the corms of a readily grown plant (Crocosmia sp.), it has potential as a
new agent for controlling blood glucose levels in diabetics and obese patients.

So, the mechanism that evolved in Crocosmia to conserve starch grains is one in which the pharmaceutical
industry is likely to show a great deal of interest, given the numbers of
diabetics and the "epidemic" of obesity in many countries. This
medical application could lead more people to think about the evolution of Crocosmia and its Natural History,
helping us to move away from our dominant anthropocentric view and towards a
sense of wonder in the capabilities of all living organisms.

Tuesday, 2 August 2016

On a recent visit to Scotney Castle, I discovered a copy of
James Johnston's The Chemistry of Common
Life among the many books in the Library [1]. It is an interesting book
that gives descriptions of the physiology of organisms and has several sections
on narcotics and their use by humans. Johnston had written on this topic
earlier and his two articles published in August and November 1853 in Blackwood's Edinburgh Magazine were re-printed
in the Journal of Psychoactive Drugs in
1985 and 1986 [2,3]. He gives us insights into the worldwide use of narcotics
up to the 1850s.

Johnson was a Scot who graduated in Philosophy from the University of
Glasgow and then pursued a school teaching career in Durham from
1825 to1830 [4]. Having made a successful marriage, he was able to leave
teaching and pursue his interest in Chemistry, including studying with
Berzelius in Sweden, and this resulted in his being appointed the foundation
Reader in Chemistry and Mineralogy at the University of Durham [4]. It was in
the field of Agricultural Chemistry that he was best known and his research
work was recognised by Fellowship of the Royal Society in 1837 [5]. In the Oxford Dictionary of National Biography,
Knight writes that:

Johnston became a successful
popular lecturer and writer.. ..His Chemistry of Common Life.. ..was a classic
popularization of up-to-date science.

Chapters in The
Chemistry of Common Life [6] on the fermentation of alcohol, and its subsequent
distillation, are followed by a section on "The Narcotics We Indulge
In" (based on the articles in Blackwood's
Edinburgh Magazine). Johnston provides a wide-ranging review of the
world-wide use of "narcotic indulgences", the most important of which
are mentioned in his concluding comments:

Siberia has its fungus [Amanita muscaria] – Turkey, India , and
China, their opium – Persia, India, and Turkey, with all Africa, from Morocco
to the Cape of Good Hope, and even the Indians of Brazil, have their hemp and
haschisch – India, China and the Eastern Archipelago their betel-nut and
betel-pepper – The Polynesia islands their daily ava [from the ground roots of Piper methysticum] – Peru and Bolivia
their long-used coca – New Granada and the Himalayas their red and common
thorn-apples [Datura sanguinea and D.
stramonium] – Asia and America, and all the world, we may say, their
tobacco – the Florida Indians their emetic holly [Ilex vomitoria] – Northern Europe and America their ledums and
sweet gale – the Englishman and German their hop, and the Frenchman his lettuce.

All these narcotics come from fungi or plants and most are
familiar to us, perhaps with the exception of the use of lettuce; the sap of
some types of lettuce being dried and powdered and used in a similar way, and
with similar properties, to opium. Johnston describes tobacco as being consumed
world-wide in the 1850s, either smoked or taken as snuff, and other narcotics
were widely available: laudanum, for example, consisted of 10% powdered opium
in 20 – 50% alcohol and was used as a painkiller and cough medicine,
some writers and artists also taking it for the effect on their powers of
creativity. The main psychoactive constituent of opium is morphine and
it was known to be addictive – Coleridge was a well-known addict whose
difficulties are described by Johnston.

"The Narcotics We Indulge In" concludes with a
summary that adopts a high moral tone, as befits someone from the Scottish Kirk
tradition:

..there exists a universal craving
in the whole human race for indulgences of a narcotic kind. This is founded in
the nature of man.. ..this craving assumes in every country a form which is
more or less special to that country. It is modified most by climate, less by
race, and least, though still very sensibly, by opportunity.. ..among every people
the form of craving special to the whole undergoes subsidiary modifications
among individuals. These are determined by individual constitution first, and
next by opportunity..

..I may remark that, with the
enticing descriptions before him, which the history of these narcotics
presents, we cannot wonder that man, whose constant search on earth is after
happiness, and who, too often disappointed here, hopes and longs, and strives
to fit himself for happiness hereafter – we cannot wonder that he should at
times be caught by the tinselly glare of this corporeal felicity, and should
yield himself to habits which, though exquisitely delightful at first, lead him
finally both to torture of body and to misery of mind; - that, debilitated by
the excesses to which it provokes, he should sink more and more under the
influence of a mere drug, and become at last a slave to its tempting
seductions. We are indeed feeble creatures, and small in bodily strength, when
a grain of haschisch can conquer, or a few drops of laudanum lay us prostrate;
but how much weaker inmind when,
knowing the evils they lead us to, we are unable to resist the fascinating
temptations of these insidious drugs!

Although Johnston admits that the use of tobacco and opiates
had become global in the 1850s, he would probably have been surprised at the
widespread use of drugs that is prevalent today and the various forms that
they take. Clearly one difference is the development of synthetic drugs
like LSD and amphetamines that are produced in chemical laboratories, rather
than directly from fungi or plants. One aspect that would not have surprised him is the
money involved in the production and selling of narcotics, as he remarks on
the world-wide size of this industry in The
Chemistry of Common Life.

The widespread use of "narcotic indulgences" for
religious purposes affects whole societies, but why do some of us become
addicted to narcotics, knowing that they can be destructive to physical and
mental health? It is hard not to adopt Johnston's position when addressing
this question, as we experiment with drugs, feel pressured by peers, want to
enhance our creativity, escape boredom, or indulge for many other reasons. Apart
from the change in the range of narcotics available, there are few differences
between the 1850s and the 21st Century in our need for what we now call
recreational drugs. Does that come as a surprise?